Numerous different techniques exist for building structures. One existing construction technique employs structural insulated panels (SIPs) to form some or all of the structure. SIPs are most commonly made of oriented strand board (OSB) skins adhesively bonded to foam cores, but are also produced with various type of concrete or cementituous facings. Cement based SIPs, often referred to as CSIPs, provide numerous advantages. For instance, CSIPs do not require separately installed exterior weather resistant finishes such as stucco or siding, or interior finishes such drywall or paneling. CSIPs are potentially much more durable than OSB based SIPs because, being cement based, their facings are not subject to dry rot, swelling from absorption of moisture, or spreading flame or smoke during fire.
CSIPs can be generally classified under one of two categories: (1) those that are produced by bonding thin, commercially available cement sheets to foam cores using an adhesive, (2) those produced by spray or trowel applying fresh cement directly to foam at a construction site where the building is being constructed, and (3) those formed by factory precasting.
The first category of CSIP is manufactured by adhesively pressure bonding commercially produced fiber cement sheets to a foam core. This system has several disadvantages. The CSIPs must have facing seams approximately every four feet of length, because that is the commercially produced with of fiber cement sheet available. These facing seams require additional interior and exterior finish work to weather proof and cosmetically conceal, and to achieve the traditional look of drywall or stucco. The seams are subject to cracking, and ongoing maintenance. Commercially produced fiber cement sheets are typically made with the Hatchek process wherein the cement is manufactured of many very thin sheets which are pressed together to form a final thickness, thus it is possible for the many thin sheets to delaminate from one another under certain conditions. The fiber cement sheets are typically produced with high percentages of cellulose fiber which can wick moisture and swell under certain conditions.
The second category of CSIP system is constructed by placing the foam core in its installed position at the construction site (e.g., positioned in an upright position in the case of a wall), and then spraying concrete material onto the foam core to form the CSIP. While this construction technique is capable of producing large, seamless panels, this approach is costly and requires significant skilled labor at the construction site to install the foam and spray the cement onto the foam core. The foam is difficult to keep straight, square and aligned as it is installed, and is easy to dislocate while applying the cement. The quality and repeatability of this construction technique is poor, since the SIP panels are constructed under the uncontrolled and often adverse environmental conditions of the construction site. The quality and repeatability of this construction technique is also highly dependent on the skill of the person applying the concrete material to the foam core.
The third category of CSIP system involves factory precasting or spraying thin fiber reinforced Portland cement facings onto relatively short foam cores, with the cured CSIP then being installed onsite similar to fiber cement CSIP panels of the first category described above. These techniques are not suitable for making large seamless panels since Portland cement is subject to significant drying shrinkage which can cause larger panels (e.g., larger than about 4′×8′) to warp, curl and crack. These precast CSIPs are also not conducive to mass production due to the relatively long curing times of Portland cement. A high percentage of expensive polymers are required to eliminate the need to wet-cure the panels and to assist the panels in bonding to the foam, as Portland cement does not naturally bond well to the types of polystyrene foam typically preferred for SIP and CSIP panels. Additionally the hydration of Portland cement results in a high percentage of calcium hydroxide being generated, which grows into and damages some types of reinforcement, such as glass fiber, thus lessening strength and ductility over time. Pozzolans such as silica fume or fly ash may be used to reduce the amount of calcium hydroxide generated, but add significantly to material cost and pose additional manufacturing challenges because they are highly respirable and damaging to lung tissue.
Thus, existing CSIP systems are costly, labor intensive to produce, have potential weaknesses or faults, have poor quality and repeatability, and/or are limited to relatively small sized panels.